Navigational system



Dec. 26, 1950 iled April 19, 19 5 NAVIGATIONAL SYSTEM '7 Sheets-Sheet 2 f l3 /28 RF j QG DETECTOR COURSE, V AMPLIF|ER V27 RECEIVER 52 FILTER f1? uncommon/ 55 souRc FILTER f,

fl'f z, 3 53 97 SYNCHRONOUS g g MOTOR g z 0 5s a $24 3 gig aMODULATOR PULS'NG i: TRANSMITTER 25 '1 cmcurr coamsra f2? RECEBVER art 0W MARCEL WALLACE W RECEIVER R.F. W 8

AMPLIFIER 7 DETECTOR FILTER AMPLIFIER j,

Dec. 26, 1950 M. WALLACE 2,535,107

1 NAVIGATIONAL SYSTEM Filed April 19, 1946 7 Sheets-Sheet 3 Q 85 E 5L6; SAWTOOTH 86 8 swEEP 8| CIRCUIT E n2 f "4 KEYING RECTIFIER 1E SIGNAL V ("a REGTIFIER COURSE RECEIVER FILTER '7 "7 f 2- Y az 83 R 1 v ECEIVER R.F. L TRIGGER AMPLIFIER cu|T DETECTOR E AMPLIFIER MODULATOR 7 mausmrnzn 4 MODULATOR A AMPLIFIER i gyvua/nm MARCEL WALLACE Filed April 19, 1946 FIG.4

BO Y (8| RECEIVER R. F.

AMPLIFIER DETECTOR AMPLIFIER M. WALLACE NAVIGATIONAL SYSTEM 7 Sheets-Sheet 4 PHASE CHANGER CIRCUIT COURSE RECEIVER KEYER I .gzJ

RECEIVER R. F,

AMPLIFIER DETECTOR AMPLIFIER POLARITY DETECTOR I 4 I I MODULATOR TRANSMITTER TRIGGER MODULATOR AMPLIFIER MARCEL WALLACE Dec. 26, 1950 Filed April 19. 1946 M. WALLACE NAVIGATIONAL SYSTEM 7 Sheets-Sheet 5 TRANSMITTER I20 F|(5 7 MODULATOR r 72w 219 ZHMOQ 2 2 200\ SIGNAL 2B1 slGNAL "xgi b AMPLIFIER H37 205 BEACON i204 27 RECEIVER I; 208;

2m 20s SIGNAL f SIGNAL 20|\ souncz AMPLIFIER 2Ia 2l4\ /2|6 2'5 MOTOR gIvuIz/I I bo b MARCEL WALLACE Dec. 26, 1950 Filed April 19, 1946 7 Sheets-Sheet 6 F|G.IO

\[Lao I 8| as sAw TOOTH RE Iv R CE E GENERATOR (H3 2 s00 BEACON KEYING ALTITUDE RECEIVER SIGJFCGAL PULSES I 1,

MODULATOR -I2o as 94 92 86c f as 86b -86a MODULATOR TRANSMITTER AMPLIFIER 82 302 T f s04 3|:

COURSE ALTITUDE T RECEIVER an glvwem bo'u MARGEL 'wALLAcE Dec. 26, 1950 M. WALLACE 2,535,107

NAVIGATIONAL SYSTEM Filed April 19, 1946 '7 Sheets-Sheet 7 Q l I (I39 80 PHASE SWEEP I E SHIFTER V GENERATOR,

REcEIvER 30o ALTITUDE PuLsES {H3 H2 BEAC N KEYING RECEIVER SIGNAL I (I20 r92 MODULATOR MODULATOR AMPLIFIER W594 l TRANSMITTER 3B INTENSITY AMPLIFIER 5'83 COURSE ALTITUDE RECEIVER IM MARCEL 'wALLAcE asaamr Nayroa'rroaiaa srs'rara Application aprii iii, rats, serial No. 663,316

to Claims. (or sis-die) This invention relates to improvements in panoramic systems for indicating simultaneously the elevations and the relative locations with respect to an airway of one or more aircraft.

It is an object of the invention to provide a system for indicating to the operator of an aircraft or to a ground monitoring station not only the presence and the relative altitudes of a plurality of aircraft, as is provided for in the system disclosed in the co-pending joint application for United States patent of Marcel Wallace and William Leu-Leang Wu, Serial Number 633,138, filed December 6, 1945, now Patent No. 2,005,314, granted April 25, 1950, and of which this application is a continuation-in-part, but to improve the latter system by providing means auxiliary thereto which enable determination of.

relative positions with respect to a given course of all the craft on the airway.

It is a further object of the invention to provide a system of the above character, in which the indications of altitude or of relative altitude may be suitably modified to provide information indicating the relation of each aircraft to an airway, or of the course of each aircraft, course information being provided by suitable beacon station.

It is well known that present day airways are conventionally set up with two or more overlapping radio beams, the cquipotential lines of intersection of the beams constituting the center line of the airway. The separate over-lapping beams may, in certain known systems, be suitably modulat..d to enable operators of aircraft to distinguish between them, and to determine a course of travel which is either to the right or to the left of the above-mentioned equipotential line or directly thereron. It has been a common practice to modulate one of the beams constituting an airway by code signals corresponding to the letter A, the other be ng modulated with signals corresponding to the letter N; the A-N signals being so timed as to interlock, whereby at the equipotential zone both signals combine to provide a continuous tone of unvarying amplitude. On the other hand, aircraft which are it) the right or to the left of the equipotential line will be provided with predominant A or N signals, depending upon whether the aircraft are to the right or to the left of the given line. It will be understood that craft flying in opposite direction along a given line may be constrained to travel on opposite sides 01' the line, in order to avoid the possibility of collision between craft traveling in opposite directions.

Another conventional type of airway is'one in which two or more overlapping radio beams may E be transmitted. the equipotential lines of intersection of each pair of beams constituting the center line of an airway, and each beam being modulated with signals of a different frequency. Instruments are provided aboard craft utilizing the beacon system for receiving radio signals deriving from a pair of overlapping radio beams and for determining the relative amplitudes of modulating signals derived from the radio signals as a measure of course deviation from the equipotential lines previously described.

There has been proposed still another type of beacon system, for use as an aid to aerial navigation, which provides for continuous indications aboard any craft utilizing the beacon system, of the angular of azimuthal relation of that craft relative to a predetermimd line of zero azimuth. This system, which the Civil Aeronautics Authority appears to favor, requires the omni-directional transmission of a carrier modulated with a cycle signal, which serves as a reference signal, and the further transmission of a rotating directional pattern of radiant energy, the rate of rotation of the directional pattern being 60 cycles, and the phase of rotation b..ing locked with respect to the phase of the reference omni-directional signal. In such a system a measurement aboard a craft of the relative phase of 60 cycle signals derivable from the rotating directional pattern, and from the signal of identical frequency derivable from the omni-directional transmission, enables determination of azimuthal relation of the craft with respect to the beacon system.

It is, accordingly, still a further object of this invention to provide means for indicating on stratoscope apparatus, such as is described and claimed in the above-mentioned co-pending application, the relationship of each craft, the altitude of which is indicated on the stratoscope apparatus. to courses such as have been above defined or to similar or analogous courses. The term stratoscope is defined to mean a device for visually indicating strata occupied by, or altitudes of, aircraft. In this manner the o'peratcr of each craft which is traveling on a given airway, or

between predetermined points, or on a predetermined area, may be provided with an indication of the relative altitudes of adjacent craft, and of the relative positions of such craft with respect to a predetermined course line, or of the directions of travel of such craft, and may be constrained to take proper measures to avoid collision with craft traveling adjacent his own craft and at a proximate altitude.

It will be understood that while airways and hum ll? bese up in a and while I have disclosed, for purposes of illustration only, the application of my novel inventions to airways and beacons of onespecidc charto such actenthatldonotdesiretobe application, but consider my inventions as disclosed'to have application'to beacon mitted.

While I have illustrated and described my system as directed to a system for transmitting paired altitude and course indications from each of a plurality of aircraft, and for receiving aboard each of said aircraft the altitude-course signals deriving from the various craft and for translating a plurality of such signals into simultaneously visible indications, it will be clear that,

' in its broader aspects my ystem may be utilized for transmitting information of other character.

if desired, in the form of paired data.

Transmission via radio, which is extremely convenient in the case of aircraft, or in the case of surface craft, may be totally inapplicable in the event it is desired to utilize my invention for transmitting information from an underwater source, such as a submarine. In the latter case, supersonic or sonic transmissions may be utilized, of a character now generally known and understood. Likewise, in the case of industrial applications, transmission may take place over wires, or transmission line or by induction as distinguished from radiation.

It is, accordingly, a further object of my invention to provide a telemetric system wherein pairs of data are traitted in the form of pulses, timed in accordance with one of the data and modulated in accordance with another of' the data.

It is still another object of my invention to provide a telemetric system wherein a variable reference value may be indicated distinct from a plurality of further indications related thereto, but in convenient juxtaposition thereto.

It is still a further object of the invention to provide indications on the face of a cathode ray oscilloscope of a, plurality of paired data, in the form of indications with respect to a pair of coordinates simultaneously.

The above and still further objects and advantages of my invention will become apparent upon study. of the following detailed description of various specific embodiments and applications of my invention, when 2 1 en in conjunction with the accompanying draws. The scope of the invention, as distinct from the specific embodiments herein disclosed, is defined in the appended claims.

In the drawings:

Figure 1 illustrates schematically and in block diagram an instrument which may be carried on aircraft. for indicating to the operator of the aircraft the relative altitudes and courses of a plurality of craft equipped with similar instruments, and for transmitting signals indicative of its own altitude and course. indications being provided by a single rotating neon cell;

Figure 2 illustrates schematically a further embodiment of the instrument illustrated in HEP? 4 apairofneonceilsior providing indicatio Figure 3.1a a schematic block diagram of a system similar to that of Figure 1 and utilizing a cathode ray indicator for providing course and altitude indications;

Figure 4 is a schematic block diagram of a further embodiment ofthe invention illustrated in Figure 8, in which course and altitude indications are provided on a circular trace on the face of a cathode ray indicator;

Figure 5 illustrates schematically a device ineluding code wheels for providing keying signals to a transmitter, which are representative of course significant potentials provided by a course receiver, and which may be utilized in the embodiment of the invention illustrated in Figure l oi'the drawings:

Figure 8 represents in schematic block diagram a device of the same general character as that of Figure 5, but in which high frequency modulation sources are substituted for the code wheels of Figures 5 and 6, and which may be utilized in the embodiments of the invention illustrated in Figures 3 and 4:

' Figure 7 illustrates schematically a further embodiment of the device illustrated in Figure 6;

Figure 8 illustrates in detail certain of the features of the devices illustrated in Figures 5 and 6;

Figure 9 is a circuit diagram of a discriminator circuit utilizable in the embodiments of the invention illustrated in Figures 3 and 4 of the drawings, and there illustrated in block diagram;

Figure 10 illustrates largely in block diagram a modification of the embodiment of the invention illustrated in Figure 3 of the drawings, and providing indications of the extent to which each of a plurality of craft may be oil! course;

Figure 11 illustrates largely in block diagram a modification of the embodiment of the invention illustrated in Figure 4 of the drawings, and providing indications of the extent to which each of a plurality of craft may be on course provided by one or more suitable beacon transmitters.

Referring specifically to Figure 1 of the drawings, there is illustrated a device which, installed in an aircraft, transmits to all craft which may be equipped with similar devices information as to the altitude of the device and of its left-right position relative to a defined course. The equipment illustrated is' further capable of simu1tane= ously receiving and translating similar information received from a one or more aircraft.

The device of Figure 1 comprises a transmitter antenna i, energized from a transmitter 2 which is tuned to a suitable frequency, the identical frequency being utilized by all similar equipments operating on a given airway. The transmitter 2 is normally quiescent and transmits only while energized by a pulse of energy provided by the pulsar I, which is controlled in turn by an altitude responsive device having the function of controlling the operation of the pulser 3.

The pulse time controlling circuit comprises an aneroid cell or similar atmospheric-pressureresponsive device 4 for positioning a rack 8 in accordance with the altitude of an aircraft, the rack [serving rotatably to position a shaft 8, from which extends radially a small permanent magnet 1. The magnet I will, by the action of the rack I and the cell 4, be constrained to take a position on the circumference of a circle, which corresponds with, and which may be calibrated in terms of, altitude.

A shaft U is rotated at a convenient relatively high eomtent speed by means of e, synchronous motor in elignment with the positionable shaft ssid shalt ceriying e coil. til, preiersbly comprising as core it, end which serves es s. voltege pich up in response to passage of the coil ill post the permunent magnet l, The pulse or" voltage provided by the coil it during its traverse of the mugnetic field provided by the permanent rnegnet i is epplied vie suitable slip rings and brushes iii to the pulsing circuit 3%.

it will be obvious that the time phase of the pulses transmitted by the equipment above described is e measure oi altitude of the aircraft carrying the equipment. This craft, us is quite common at the present time, may be equipped with n, beacon receiver end indicator, for indicat- 7 ing whether the credit is traveling to the right or the left of s given course, or directly on that course, in response to suitable radio beacon signals, which are supplied in conventional manher along the airway.

One type of course indication, which is well known to the art and therefore requires no detailed elucidation in this specification, involves two overlapping rsdio beams, the beams being respectively modulated in interlocked A-N rhythm. Reception aboard e. craft of a, series of coded letters A indicates that a. craft is on one side of the course line, whereas reception of u series of coded N signals indicates position on the other side of the course line. The A and N signals interlock to provide a cont nuous unmodulated tone signal when the craft is directly in the center of the course.

In accordance with the present invention, a course receiver I3 is provided, which receives A-N signals and applies same to a modulator M via line l3, while manual switch I6 is closed. The modulator I 4 serves to energize the transmitter 2 in accordance with the A-N rhythm of the signals provided by the receiver l3. Thereby the pulse output of the transmitter 2 is modulated in such manner as to provide information as to the side of the radio beacon course occupied by the signaling craft.

Mounted on the shaft 8 and rotating cophasally with the pick-up coil III, is a neon filled indicator cell H, which may be supplied with signal via the slip rings and brushes l8. The

cell l1 may be coupled to the transmitter 2 via a line having connected therein a coupling condenser 20 and a manually operated switch 2|.-

The pulse rate of the transmitter 2 is normally sufllciently great to provide an apparently continuous illumination of the cell I! at one point in its circular path of travel. The modulation provided by the modulator [4, however, interrupts the continuous illumination of the cell I! in AN rhythm, to indicate on which side of a course line the transmitting craft is located.

For convenience of observation the cell I! may be provided with a. disk 22, rotated by the shaft 3 and comprising a narrow elongated slot 23 opposite the cell II.

The disc 22 rotates with respect to a scale 24 which may be secured to the casing 25, whereby interpretation of theungular position of the cell II when illuminated may be readily accomplishcd. I

It. z-c

- that a. plura ity of aircraft on a. common airway are provided with apparatus such as is schematically illustrated in Figure l of the drawings. The synchronous motors 3 aboard the vairious craft are synchronized by means or any suitable synchronizing system m it? known in the art, and rotute the see filled cells it end their ussociuted discs in onset time synchronisstion and in phase. Pulses trsnsmitted by the various aircraft are intercepted by the antennas tit, amplified by the amplifier 2!? end detected in the detector Detected pulses ere applied to the cell ll vie the line the points in the cycle of rotation of the cell it st which illumination occurs being indicative oi the altitudes of the various croft, and the modulu= tion of that illumination in A or N rhythm indiceting the location of each of the craft with respect to a course line.

since courses may be set up ulong slrweys in. various ways, the A-N system above described being but one such, I have provided devices tor suitably modulating the transmitter 2 in uccordonce with left-right course indications which msy operate independently of the character of the beacon signals. It is customary for beacon receivers operating in conjunction with various types of beacons now known in the art. to be ur== ranged to provide output signals of one polsrlty in response to signals originating on one side ot a given course, and signals of the opposite polurity in response to signals originating on the other side of the given course. Such signals may be applied to a left-right indicating meter for providing visual course indications.

In the present application the signals of positive and negative polarity are applied to a. device, illustrated in Figure 5 of the drawings, and comprising polarized relay 33, which actuates an armature 31 in a direction dependent on the polarity of said signal. The armature 33 operates a switch 32 connecting one of two sources of modulating signals to the output 33 of the keying device.

The modulating signal sources comprise a source of potential 34, having its negative terminal grounded and its positive potential connected in parallel to a. pair of coding wheels 33 and 36. Wheel 35 is provided with a. series of contacts each covering a few degrees of arc, and separated by spaces covering a. considerably greater are. The wheel 36, on the other hand, is provided with a series of contacts each about three times as long as the contacts on the wheel 33 and separated by relatively short spaces.

The wheels 35 and 36 may be so constructed and arranged that the dots on wheel 35 are equal in length to the spaces on wheel 36, and the clashes on wheel 36 to the spaces on wheel 35. Further, the dots and dashes on wheels 35 and 36 respectively may be timed to interlock exactly.

Potential is applied to the wheels 35 and 35 via brushes and slip rings 31 and 38, and modulating signals are derived from the wheels 35 and 36 by means of wiper contacts 33 and 40 respectively, which are connectable selectively or simultaneously with the output terminal 33 by means of the switch 32.

Referring now again to Figure 1 of the drawing, and with the switch Is there illustrated in open position, course signals supplied by the receiver l3 in the form of potentials of zero, positive or negative polarity may be applied to the keying signal generator l3, and may control some to provide selectively output modulating potentlals in the form of a series of dots separated by dashes or alternatively a series of dashes separated by dots, the alternative outputs being indicative of right-left locations of the craft. and being supplied to the modulator ll to modulate the output signal of the transmitter 2. Should the output asses oi the ver It be a zero potential or a small potential of either polarity, indicating a substantially on-course condition, the device I. will provide a continuous potential to the modulator ll, enabling the transmitter is remain in continuous pulses operation.

Reviewing briefly the operation of the modification of the invention illustrated in Figure l. of the drawings, equipments installed aboard each of a plurality of craft provide radio tr in the form of pulses, the pulses being equally spaced and phased at each craft with respect to a predetermined starting time in accordance with the altitude of the craft. The equipments aboard each of the craft are suitablysynchronized. and provide indications of the phases of all received pulses, the indications being translatable in terms I of altitude. Each craft further receives course signals from a beacon transmitter, or a series of such transmitters, located along an airway, and

is provided with equipment suitable for translating the indications provided by the beacon re-, ceivers into modulations which may be superposed on the pulses transmitted by that craft. A suitable receiver-indicator aboard each craft receives the signals transmitted from all the craft and translates same into a simultaneous display of thte altitudes and course positions of the various craf Figure 2 illustrates still a further type of stratoscopic device which is supplied with means for transmitting and indicating whether each of a plurality of aircraft are traveling to the right or the left of a given course line or are substantially directly on course.

In the system of Figure 2, as in that of Figure 1;

an aneroid cell or similar device 4 controls a rack 5 which positions a shaft 8 bearing a small permanent magnet l to an angular position which is representative of altitude.

A shaft 9, aligned with the shaft 6, is rotated by means of a drive means 9 synchronized in the various craft involved. A pick-up coil l0 supplied with a core ii is rotated adjacent the circular path which may be described by the magnet i and in its transit past the magnet i, a potential pulse is induced in the coil it the phase of which is representative of the position of the magnet l and consequently of the altitude indicated by the cell A.

- Successive pulses of voltage generated in the coil it in its periodic and rapid rotation are applied to a pulsing circuit 3 via suitable slip rings and brushes l2, and serve to modulate a transmitter 2, which transmits a series of relatively. high radio frequency pulses for reception by all craft in the vicinity which may be properly equipped.

A beacon receiver it receives and detects signals indicative of the relation of the aircraft to an airway and supplies, at its output, potentials having a value and a, polarity indicative of the relation of the aircraft to the course, in well known manner. The output of the receiver is is applied to a modulation source 56, which provides at its output modulating signals of one of two distinctive frequencies f1 and is, dependent upon the side of the course occupied by the receiver I3, and of both frequencies .11 and is should the craft carrying the receiver It be traveling substantially directly on course. The frequency or frequencies provided by the modulation source BI maybe applied to a modulator W. for further application to the tratter 2, whereby each 8 transmitted pulse maybe modulated with course I en if ing si nals ti and/or 1:.

Modulated pulses transmitted from a plurality of aircraft, and indicative. of the altitude and course of said aircraft, may be intercepted by the antenna 20, amplified in-a suitable amplifier I! and detected ina detector II, to derive from the received modulated carriersa series of timed modulated pulses, indicative in respect to their timing of the altitudes of the transmitting craft, and indicative in respect to the modulations on are pulses of the courses of the transmitting cra Connected in parallel to the output of the detector 28 is a pair of filters I2 and 58, one of which is arranged to pass only the frequency 11 and the other of which is tuned to pass only the frequency 12. The filter 53 is connected at its output to a neon cell I1, and the filter 52 to a neon cell Ila, via suitable slip rings and brushes I8, the cells I1 and Ila being mounted for rotation on the shaft 8.

For convenience of observation the cells I1 and Ila may be provided with a disc, secured to the shaft 8 for rotation therewith, and provided with a, pair of narrow elongated slots 23 and 23a associated respectively with the cells I1 and Ila. The disc 22 rotates relatively to a reference scale 24 which may be secured to the casing 25, whereby interpretation in terms of altitude of the angular positions of the cells ll and Ila, when il1uminated,'may be readily accomplished.

Reference is herewith made to the co-pending application of Wallace et al., Serial No. 633,138, filed December 6, 1945, for complete and detailed information concerning the structure of the indicator, and which is illustrated schematically in Figure 2 of the present application in sufilcient detail for the purposes of the present application.

It will be apparent from the preceding description, that the cell Il will be illuminated at an altitude indicative position in response to signals transmitted from craft on one side of a given course line and that cell Ila will be illuminated likewise for signals transmitted from craft on the other side of said course line, both cells being illuminated in response to signals originating from substantially on-course craft.

In order to avoid blocking of the receiver 21 by signals originating at the transmitter 2, a desensitizing signal is applied to the amplifier tl via the lead 54 in accordance with well known practice, the desensitizing signal being derived from the pulser 3, and serving to reduce appreciably the gain of the amplifier 21. It is desirable, nevertheless, that signals originating in the transmitter 2 be indicated at the cells N, Na and that such signals be identifiable as to their point of origin.

There is, accordingly, provided a circuit from the pulser 8 via an isolating resistance 55 and a rotating switch 58, to the cell Ila. The rotating switch 58 is driven by suitable gearing 51 from the shaft 8, and rotates at a lower rate of speed than does the shaft 8, a suitable step-down ratio for the gearin being 1:25. The rotating switch 56 is provided with a peripher which is in part non-conducting and in part conducting, in order periodically to interrupt the circuit between the pulser 3 and the cell Ila, and because of the non-integral relation between the speed of rotation of the switch 56 and the shaft t, the illumination of the cell Ila will be interrupted at relatively random intervals. whereby pulses originating in the transmitter 2 may be readily identified as such and distinguished from those derived from the receiver Il, these latter providing illumination continuously. in accordance with the character oi the course-significant modulations impressed on the received signals.

A single-pole single throw switch "a, conneoud in the output circuit of the fllter 58 may be opened when it is desired to identity locally originating signals. serving to isolate the cell ila irom its normal source oi signal, 1. e.., the filter It, and to connect the cell Ila solely to the pulsing circuit 3 via the switch It. Thereby one of the plurality oi steady visual indications some- 7 times present on the face of the disc 22, and due to the cell Ha, may be supplanted by a ilichering indication, upon opening switch 85. or alternatively. ii the course position oi the local craft should be such as to provide no modulation signal ior the cell I is, that cell will, nevertheless, be provided with a flickering signal from the pulsing circuit 3 and the rotating switch so.

Referring now to Figure 6 oi the drawings, there is provided a schematic circuit diagram of a modulation generator controllable in response to the output of a course receiver 27 to provide suitable modulating signals for utilization in the device illustrated in Figure 2 of the drawings, and there identified as a modulation source M.

The output of the beacon receiver 21. and comprising a zero. positive or negative signal. in accordance with the location of the receiver with respect to a predetermined course. may be applied to a polarized relay 30 which actuates its armsture ll in a direction dependent on the polarity oi the output oi the beacon receiver 21.

The armature 3i actuates a switch arm 32, which in its actuated position provides a circuit to the leads a and I selectively, the latter being output leads for the signal sources 48 and 40 respectively. The signal sources ll and 4! may be sources of alternating current oi suiliciently high frequency to enable modulation of pulses transmitted by transmitter 2, of the order of 1 The frequencies generated by the sources 11 and fa, further. should not be integrally related, to avoid filtering diiilcuities and false filter responses.

The construction of the switch 82 which is illustrated schematically in Figures 5 and 7 is illustrated in detail in Figure 8, which shows the armature 3i pivoted at I and actuating a switch arm 82 constructed-oi electricity conductive material. The two contacts I and 43 are connected to suitable leads, such as l and 40 are preferably constructed of copper and have tungsten or silver beads 44, l! of hemispherical shape.

To the end oi. the switch arm 82 are secured a pair of diverging spring contacts 48 and 41, one oi which, ll, normally contacts the head 44, the other 41, being normally in contact with the head 48. Upon actuation oi the switch arm 32 by the armature 3| one oi the contacts 46, 41 may be opened, the other. however, remaining in circuit closing position. By mean of this expedient. it is possible to connect to the output terminal as either of two signal sources which may be conneci'edtotheleadsflandltorbothslgnal sources, but both sources can never be simultaneously disconnected.

The navigational system illustrated in terms of the apparatus of Figures 1 and 2, and depending upon rotative neon cell indicators and me,-

intermsoipulsersandindicstorsoian character and utilizing cathode ray tube indicators and electronically timed pulse generators. the general organization of the latter system being illustrawd schematically in Figurw 8, 4. l0 and 11 of the drawings.

neierringnowtoFiguresoithedi-awim, there is illustrated schematically a circuit diagram 0! a stratoscope system for indicating simultaneously the altitudes oi a plurality of air crait as well as the positions thereof with respect to a given course, the indication being provided on the lace oi a cathode ray indicator 0B in terms oi a series oi horizontally extending pips P on a vertical trace on the indicator. Pips appearing on both sides oi the trace simultaneously indicate an on course craft; pips appearing on the left of the trace indicate a craft to the left of the course and pips appearing to the right of the trace indicate a craft to the right of the course.-

In the practice of my invention in accordance with the embodiment thereof illustrated in Figure 8 of the drawings, a carrier modulated with a convenient synchronizing signal is transmitted from a convenient location, which may be on the ground. The synchronizing signals are transmitted on a distinctive frequency to prevent interierence with other signals used in the system. and are intercepted by the antenna 89 and suitably amplified and detected in the receiver 8!. The output oi the receiver 8| consists oi synchronizing signals which are applied to the sawtooth sweep generator 8! to synchronize the sweep signals generated thereby and applied to the vertical plates of a cathode ray oscilloscope denominated generally by the numeral 86. The sawtooth voltage emanating from the generator 88 is similarly applied via blocking condenser I 08 to the grid I" of a tube I00 which is supplied with plate voltage irom a source I", and is plate loaded by the resistor MI. The plate I of the tube I" is connected via coupling condenser m to the input of a trigger circuit II which supplies short pulses to the amplifier 92 for application as modulating signals to the transmitter 08, having an antenna 04.

The tube Hill is normally biased back beyond cutoil! by a potentiometer circuit, denominated generally by the numeral H0 and comprising the battery 81 or other voltage source, grounded at its positive terminal, and connected in series with a pair of resistors 96 and III, the latter being variable, to enable adjustment of the system to provide a zero indication at sea level. The contact 9i rides over the resistor 96 and taps therefrom a negative voltage which is proportional to altitude, the contact 95 being actuated by an aneroid cell 4 or its equivalent. The adjustable resistor It! serves to set up a minimum negative bias corresponding with sea level.

The sawtooth voltage provided by the generator II and applied to the grid I06 0! the tube I" is of positive polarity, and is adapted to overcome the negative potential normally present at the contact 86 at some point in its growth cycle, the relative time in the cycle at which the opposing voltages balance being determined by the magnitude oi the negative bias to be overcome, and said relative time being thus a measure of altitude. As the cut-oil bias on the grid I" of the tube I is removed plate current flows in the tube and a signal is applied via condenser Ill to the trigger circuit 9| to trigger same to produce a signal Pulse.

ehanicallv actuated pulsars finds a counterpart It It will be reoosniaed that a plurality of trait each equipped similarly with synchronized sawtooth generators 33, will provide each a series of periodic equally spaced pulses the relative times of transmission of which with respect to the synchronizing pulse provided by the receiver 3|, and which is common to all the craft. is in correspc;idence with the altitudes of the transmitting era t.

The transmitter 33 aboard each craft is not only pulse modulated by altitude significant pulses, but each pulse contains further tone or tones modulation provided by a tone keyer H2, corresponding in detail with either of the tone keyers illustrated schematically in Figures 5 or 7 of the drawings, and controlled by a beacon receiver I I3 having an antenna I ll.

Received altitude and course significant signals are received on an antenna 32 and suitably amplified and detected in the receiver 33. Output signals in the form of short spurts of tone are applied to one horizontal deflecting plate 36a via line HI, tone filter H1 and rectifier Illa, and to the other horizontal plate 38b via the line I IS, the filter H8 and the rectifier Ilia. The filters Ill and H3 respectively may be designed to pass frequencies 11 and fa.

The face of the cathode ray indicator 80 w provide, in accordance with the arrangements described and illustrated, a vertical altitude trace, having right and left pips for aircraft which are traveling directly on course. pips to the right of the altitude line for craft on the right of the course line, and pips on the left oi the altitude line 'for craft on the left of the course. The vertical positions of the pips are indicative of the altitude of the various craft, and the face of the indicator 36 may be suitably calibrated to enable this quantity to be read ofl directly.

While I have illustrated in Figures 5 and 6, and described in preceding portions of the specification, certain forms of modulation generators, responsive to beacon signals, one of which is suitable for establishing and interrupting pulse sequences, whereas the other is suitable for modulating each transmitted pulse with an accompanying alternating current signal, it will be recognized that the systems heretofore described are mechanical circuit makers and breakers in character and present no possibility of providing course indicators capable of providing information of the extent to which the various craft employing the system may be off course.

Modifications of the systems illustrated in Figures 3 and 4 of the drawings, and utilizing a novel keying circuit illustrated in Figure 7 of the drawings, as the keyer H2 of Figures 3 and 4, enables transmission and indication of signals representative of the extent to which aircraft are oil? course. Embodiments of such systems are illustrated in Figures 10 and 11 of the drawings, respectively, the source of keying signal H2 provided in the output of the beacon receivers H3 of Figures 10 and 11 corresponding with the device schematically illustrated in Figure '7 of the drawings.

Referring now specifically to Figure 7 of the drawings, there is illustrated the beacon receiver H3 having connected across its output a resistor 204, having its central point grounded and providing at its end points 205 and 206 potentials of respectively opposite polarity, the specific polarity assignable to the points 205 and 206, as well as the magnitude of the potentials, being dependent upon the location of the receiver H3 with respect to a predetermined beacon course i2; established in terms of overlapping'radio beam! by means of a suitable beacon transmitter.

A pair of signal sources 200, 20I generate respective signal frequencies 11 and I: of equal amplitudes, each of which may be distributed in two distinct paths to the respective signal amplifiers 202, 203. Upon closure of manually operable switches M3, the cbde wheels 200, 2I0 may be short circuited by the leads 2", 2I3 and 2I8, 2I3

respectively, and the outputs of the signal sources 200 and 20i applied directly to the input terminals of the amplifiers 202 and 203.

With switches 2I5 open signals generated by sources 200 and 2M are applied to the signal amplifiers 202 and 203 respectively after being chopped by the code wheels 209 and M0. The latter code wheels are provided one with a series of spaced dots 2H and the other with a series of spaced dashes 2l2, so arranged with respect to one another as to provide interlocking signals to the amplifiers 202 and 203.

The voltages provided at the end points 203, 203 of the resistor 204 are applied a gain control potentials respectively to the amplifiers 202 and 203 via leads 201 and 203, whereby the amplitudes of the signal outputs provided by the signal amplifiers 202 and 203 are differentially controlled in accordance with the output of the beacon receiver H3.

Since, in the embodiment of the invention illustrated in Figure 3 of the drawings, as well as in the embodiment illustrated in Figure 4 thereof, the magnitude of the pips corresponding to course indications is dependent on the magnitude of the signals utilized to produce the pips, it will be clear that utilization of signal sources I I2 of the character illustrated in Figure '7 of the drawings in the systems disclosed in Figures 3 and 4 of the drawings, will enable indication of the extent of deviation of aircraft from a predetermined course to be presented in these systems.

In Figure 4 of the drawings, I have illustrated an embodiment of my invention which utilizes a polar type of cathode ray indicator, altitudes being indicated in terms of location of pips on a circular trace. Right, left indication is provided in terms of inward and outward pip deflections respectively, on course being indicated by simultaneous inward and outward pips.

In the embodiment illustrated in Figure 4 of the drawings, the receiver 8i having an antenna is utilized for receiving and demodulating a carrier modulated with a low frequency pure sine wave, preferably of about 60 cycles as well as a synchronizing pulse at the same frequency. The demodulated sine wave signal is applied to the plates of a polar cathode ray tube I30 via a circuit I3I comprising resistor Hill: and condenser I3 I b, arranged to provide a rotary sweep of the beam of the cathode ray indicator I30. The various aircraft equipped with apparatus constructed in accordance with the embodiment of Figure 4 of the drawings are, in this manner provided with synchronized circular sweeps. Each individual craft may vary the relative phase of its sweep by means of the phase changer I32 interposed between the receiver 8| and the phase splitting circuit I3I, in order to align pulses originating in the transmitter ill of the local craft with the zero of a circular scale calibrated in terms of altitude, whereby all other signals representative of the altitudes of foreign or remote aircraft may be indicated in terms 13 of altitude relative to the local it. rather than in terms of absolute altitude.

In order to provide assurance of accurate syn-- chronizations of the sweep circuit voltages. aboard all the craft and to provide indications of absolute altitude, the start of the sweep circuit voltage may be aligned with a zero marker on the face of the indicator by adjusting the phase shifter I82 until the winning synchronising pulse is aligned with the said marker, as explained in the co-pending application of a et al., No. 833,138 filed December 6, i945.

Pulse present in the output of the receiver Ii are applied to control a sawtooth wave generator its, initiating successive sawtooth sweep voltages which are synchronized and in phase for all craft utilizing the system. it

The sawtooth wave generated by the generator lie is applied, as in Figure 8 of the drawings. to a potentiometer arrangement lili, com voltage source ill in series with resistors 98 and ill. the positive terminal of the voltage source being grounded. and a variable tap at being provided to apply negative bias voltage to the grid Hit of the tube m. The position of the tan 9! is controlled to be representative of altitude, being actuated by an aneroid cell or similar device 4. The voltage provided by the sweep circuit generator I39 serves to balance the negative bias of the potentiometer circuit lit. at a point in the growth curve of the sawtooth voltage which is determined by altitude, the tube I thereupon becoming conductive and transmitting a signal to the trigger circuit 9! via the blocking condenser Iii'l to course the trigger circuit 9| to generate a pulse of voltage. The output of the trigger circuit 9! is applied to the modulator amplifier 92 which controls the transmission from the radio transmitter 98, the latter comprising the antenna 94.

Since a plurality of craft utilizing the present system may be similarly equipped, each craft will transmit a signal timed, with respect to the synchronizing pulse supplied to all the craft, so as to indicate altitudes of the craft. The short spurts of R. F. signal transmitted by the transmitter 93 may be further modulated by signals derived from a keyin generator H2 and applied to the transmitter 83 via the modulator.

The internal structure of the keying generator H2 is adequately indicated in Figure 5 of the drawings. the device being arranged as has been heretofore explained, to provide tone modulation of one frequency upon reception of course signals in the course receiver H3 originating on one side of a given radio course, and of a radically different frequency upon reception of course signals originating on the other side of the said course. On course signals are represented by both signals simultaneously.

The tone modulated and pulsed R. F. signals transmitted by each of the plurality of craft involved in the system are received in a receiver 83 having an antenna 82, and are applied to a polarity detector which provides an output signal applicable to the polar electrode I38 oi the cathode ray indicator I30, to provide inward or outward pips on the circular trace on the screen of the indicator I" in response respectively to tone frequency {1 or fa. Should both tone frequencies be present both an inward and an outward pip will be presented.

The polarity detector is a device suitable for producing pulsating direct current output of polarity which depends upon frequency. One emis bodiment at a suitable device ior accom lishing this purpose is illustrated mhematically in Fig- .pass tone )1 and I: only, the output sides of the filters Me and I being connected in serice with a pair of diodes MB. use and having the cathode Minot the tube its connected to the plate MB of the tube I48. The Junction point Ili between cathode Ill and plate 14s is connected to the center point of the secondary winding M2 and there grounded. The point in is connected to the polar electrode use of the indicator I80.

It will be obvious that reception of signals at frequency n will result in positive potential with respect to ground at the point ibi, whereas reception of signals at frequency is will result in negative potential with respect to ground at point Iii. Reception of both signals h and is simultaneously will not, however, result in a balanced potential at the point iii because of the difference in frequencies of the applied signals, and the output at point. ill will consist of apotential having an alternating character.

The polar electrode I88, in response to negative pulses. produces an outward pip in the circular trace on the face of the indicator. and an inward pip in response to a positive pulse. A1- ternating potential produces a double pip, extending inwardly and outwardly.

Referring now specifically to Figure 10 of the drawings. there is illustrated in schematic block diagram an instrument useful in navigational systems for roviding indications of the altitudes and courses of a plurality of aircraft, each of the aircraft transmitting pulses timed in accordance with altitude and modulated in accordance with relation of the craft to a predetermined radio course line defining an airway and provided by means of one or more radio beacon systems.

In the navigational system employing the instrument illustrated in Figure 10 of the drawings. synchronizing pulsed radio signals provided by a ground station to all aircraft utilizing the system are received in the receiver 8i, provided with an antenna so. and there amplified and detected to provide output pulses for application to the sawtooth generator 85 for purposes of synchronization. The sawtooth sweep voltage produced by the generator 85 may .be applied to the vertical plates 880 of a cathode ray indicator 88, to produce a vertical trace on the face thereof in correspondence with the sweep voltage. The trace referred to may be de-intenslfied to be vanishingly light or may be rendered completely invisible by the bias grid 6 of the tube 86, which is grounded normally by means of the lead iii.

The sweep voltage is likewise applied to the altitude pulser 300. which may be substantially a duplicate of that illustrated in detail in Figures 3 and 4 of the drawings, and causes generation of pulses timed to correspond with the altitude of the instrument. Pulses provided by the device 300 are applied to modulator 92 to cause pulsed transmission of a radio-frequency carrier from the transmitter 88, having an antenna 94.

The transmitted pulses are further modulated with signals provided by a modulator I20. controlled by a beacon receiver ill and a keying signal source Ill, the specific circuit details of which are illustrated in Figure 7 'ofthe drawings.

and which has been fully described in preceding ortions or the specification.

Modulated pulse signals emanating from each of a plurality of aircraft and representative of the altitudes and courses of said aircraft are received in a suitable course-altitude receiver ll having an antenna 82, and are there suitably amplified and demodulated to produce spurts of modulation {1 and/or la, timed to correspond with altitude, the modulation intensities or amplitudes of signals 11 and I: being representative of course deviations of the craft originating the signals.

The modulation signals 11 and I: present in the output of the receiver ll are applied to a transformer primary 30I, for inductive transfer to a pair of series connected tuned secondary coils, 302 and 303, peaked respectively at the frequencies h and f1, and having their junction point grounded.

Across the secondary windings l! and 803 are connected a pair of diodes I04 and 306 in pushpush relation, the cathodes of the diodes lll, 308 being interconnected by resistors I00, 301 having their common point grounded, the resistors being by-passed for modulation frequencies 11 and I: by the condensers 000 and 000.

The cathodes of the diodes lll and 305 are further interconnected by means of a pair of resistors ll I, lll connected in series, and the common point of which is connected to ground via a resistor lIl.

A D. 0. pulse voltage will be developed across the resistor lll, proportional to the arithmetic sum of the pulse voltages developed across the resistors 3H and m, in obvious manner, and this voltage may be applied via lead lll to the intensifier grid 3 I l, to produce a visible or intensifled dot on the face of the indicator schematically represented at ll.

The D. C. voltages produced at the resistors III and SI: respectively are indicative each of the amplitude of the modulating signals [1 and fa, and these voltages are applied to the horizontal plates 80b and 860 respectively. to produce a deflection the magnitude and direction of which depends upon the relative amplitudes of the voltages. Should the signals ]1 and I: be of equal amplitudes. indicative of an on course condition, the D. C. potentials applied to the plates 06b and llc will balance and produce no deflections. Intensiflcation will, however, be produced in any event, whence an undeflected dot may be considered indicative of an on-course condition of the craft aboard which the signals originate.

In still another embodiment of the invention, illustrated schematically in Figure 11 of the drawings, signals transmitted from a ground station and modulated with a low frequency sine wave signal suitable for establishing a rate of rotation for cathode ray indicator I30, as well as with a pulse synchronizing signal for the instruments aboard the various aircraft, is received on the receiver iii.

The receiver 8| abstracts from the received carrier wave the superimposed sine wave modulation as well as the pulse, applying same to an adjustable phase shifter I32 which may serve to vary the phase of the low frequency modulation without affecting the pulse.

The pulse may be applied to sweep generator I 39, as in Figure 10 of the drawings, and serves, as has been heretofore explained to produce pulses time modulated in accordance with altitude for transmission by transmitter Ill and antenna ll. The pulses are further modulated with keying signals provided by a keying signal source Ill, under the control of a beacon receiver Ill.

The low frequency modulation provided at the output of the phase shifter Ill is applied to a phase splitting circuit comprising resistor Illa and capacitor IlIb in series, the voltages which are applied to the vertical and horizontal plates of the cathode ray indicator Ill. to produce a circular trace. The starting point of the trace may be aligned with the occurrence of the synchronizing pulse by adjusting phase changer Ill, to align a pip produced by the pulse with a point of reference corresponding to zero altitude on a suitably calibrated circular scale.

Pulses received at the antenna ll are detected in course-altitude signal receiver ll, the modulation frequencies on the pulses being transferred by primary coil lll connected in the output of receiver 02 to tuned secondary coils lll and lll which may be tuned to frequency is and h respectively so that secondary lll passes only i nals of frequency f1, while secondary Ill passes only signals of frequency is. r

The signals present in the secondaries lll, lll are rectified by diodes Ill and Ill, which are connected cathode-to-plate, in series, a load resistor 306 by-passed for frequency I: by capacitor lll being provided for the diode 004, and a similar load resistor 301, by-passed for frequency 11 by capacitor so: being provided for diode lll.

Connected across resistors lll and III is a like pair of resistors III and III, connected in series, the point of junction of the resistors lll, 001 being connected to the point of Junction of the resistors ll I, ill by means of a resistor ill.

The voltage existin across the resistors lII, lIl in series will be at all times additive and proportional to the arithmetic sum of the magnitudes of the signals f1 and Is.

On the other hand the potential existing across the resistor lI0 is compounded of a diflerence of two potentials occasioned by current flow in the tubes 0 and 005, and hence is proportional to the algebraic diilerence between the magnitudes of the signals 11 and 1:.

The voltage across the resistors III and 3|! in series is amplified in the amplifier Ill and thence applied as intensifier signal to the intensifier grid 3 of the tube I30, which normally is biased Just short of cutoff, so as to provide but a faint trace on the face of the cathode ray tube Ill. Intensifying voltage from the amplifier lIl is of pulse duration, and results in production of bright dots in the faint trace. to indicate the presence of signals.

Voltage derived from the junction point of resistors 3H and BI! is applied to the polar electrode Ill of cathode ray indicator I30 to produce inward or outward deflections in the circular trace on the face of indicator I30 in accordance with whether the resultant or diflerence polarity across resistor lI0 is negative or positive, the magnitude of the deflection being proportional to the magnitude of the applied voltage.

Should the magnitudes of signals f1 and I: be equal, the potential applied to the polar electrode I36 will be zero resulting in an undeflected but intensified indication on the face of the indicator, this condition obviously corresponding to an on-course indication.

The relationship between the embodiments illustrated in Figures 3 and 10, and between the embodiments illustrated in Figures 4 and 11 will be obvious, the primary distinction residing in the utilization of intensifying techniques in the embodiments illustrated in Figures and 11 of the drawings, the traces provided on the indicators of Figures 3 and 4 of the drawings being of constant intensity.

While I have described a number of specific embodiments of my invention. it is obvious that modifications may be made in the general arrangement and combination oi each of the embodiments, and that equivalents may be substituted for various of the elements and sub-combinations illustrated and described. without departing from the spirit of the invention or the scope of the appended claims.

What I claim and desire to secure by Letters Patent of the United States is:

1. A navigational system comprising unitary means for indicating the altitudes of each of a plurality of craft, and said unitary means comprising further means for indicating the lateral positions of said plurality of craft with respect to a predetermined course.

2. A navigational system comprising means for simultaneously indicating the altitudes of each of a plurality of craft. and means for simultaneously indicating the relation of each of said plurality of craft to a predetermined course line.

3. A navigational system comprising means located on an aircraft for transmitting pulse signals phased to berepresentative of altitud and means for modulating said pulse signals to be representat-ive of the location of said aircraft laterally with respect to a predetermined course line.

4. A navigational system comprisin means for receiving aboard one aircraft signals each from a plurality of aircraft. said signals being modulated in respect to both altitude and course of an aircraft. and a single indicator for simultaneously visually indicating the altitudes and courses represented by said'plurality of signals.

5. A navigational system comprising means for receiving aboard an aircraft signals representative of the position of said aircraft relative to a predetermined course line, means aboard said aircraft for generating pulses carrier, means for timing said pulses in accordance with altitude of said aircraft, means for modulating said pulses in response to signals received bv said means for receiving.

6. A navigational system comprising means aboard an aircraft for transmitting pulse time modulated signals indicative in respect to their pulse timing of the altitude of said aircraft and further modulated in accordance with the position of said aircraft with respect to a predetermined course line, and means for receiving and translating said signals into visual indications each representative of both said altitude and said position of one of said aircraft.

7. A navigational system comprising means aboard each of a plurality of aircraft for transmitting altitude and course significant signals. and a receiver indicator for receiving and translating said signals into a simultaneous display of the altitudes and courses of said plurality of aircraft.

8. A navigational system comprising means aboard at least one aircraft for transmitting altitude and course significant signals, and a single indicator means located remotely from said at least one aircraft for translating both said altitude and said course significant signals into a sini8 gle indication representing simultaneously both altitude and course.

9. A navigational system comprising means aboard at least one aircraft for transmitting altitude and course significant radio signals, and cathode ray receiver indicator means located remotely from said aircraft for receiving and translating said signals to provid indications of the altitude and course signified thereby.

10. A navigational system comprising means for transmitting signals defining a predetermined course, means aboard each of a plurality of aircraft for receiving. and translating said signals to provide course significant indications, a radio transmitter aboard each of said plurality of aircraft for transmitting position reporting signals. means for modulating said position reporting signals with altitude significant modulations and with further modulations controlled by said course significant indications, means aboard each of said plurality of aircraft for receiving said position reporting signals transmissions from said radio transmitters aboard each of said plurality of aircraft and for translating said modulations into substantially simultaneous unitary indications of the relative altitudes and courses of said plurality of aircraft.

11. A navigational system in accordance with claim 10 in which said means for translating said modulations comprises a cathode ray indicator.

12. A navigational system in accordance with claim 11 in which said means for translating said modulations comprises a rotating neon cell.

13. A navigational system for aircraft comprising a transmitter aboard an aircraft, means for pulse modulating said transmitter with pulses timed to represent altitude of said aircraft, means for modulating said pulses with signals significant of courseflown by said aircraft, remote means for receiving said pulses and for providing altitude significant indications in response thereto, and means for modifying said altitude significant indications to indicate said course.

14. A navigational system in accordance with claim 13 in which-said means for pulse modulating said transmitter comprises a magnetic element positionable on the arc of a circle in accordance with altitude, and a further magnetic element mounted for rotation adjacent ,said circle.

15. A navigational system in accordance with claim 13 in which said means for modulating said pulses comprises a beacon receiver and means responsive to the output of said beacon receiver for generating said course significant signals significant of course flown by said aircraft.

16. A navigational system in accordance with claim 13 in which said means for providing altitude significant indications comprises a cathode ray tube indicator, and means for modifying said altitude significant indications comprising a circuit responsive to said signals significant of course.

17. A navigational system in accordance with claim 13 in which said means for providing altitude significant indications comprises a cathode ray indicator having means for producing a cathode ray and for controlling th intensity of said ray, means normally reducing said intensity, and means controlled by said means for receiving for increasing said intensity in response to each of said pulses.

18. A navigational system in accordance with claim 13 in which said means for providing altitude significant indications comprises a cathode ray indicator having means for producing a cathl9 ode ray and for controlling the intensity of said ray, means normally reducing said'intensity, and

means responsive to reception of signals by saidmeans for receiving for increasing said intensity, and in which said means for modulating said altitude significant indications comprises means for deflecting said ray.

19. A navigational system in accordance with claim 13 in which said means for providing altitude significant indications comprises a cathode ray tube indicator having means for producing a circular trace on the face of said indicator and means for modulating said trace.

20. A navigational system for transmitting from each of a plurality of aircraft signals having a characteristic significant of altitude, means aboard each of said aircraft for modulating altitude significant signals transmitted therefrom with further signals significant of lateral positions of said craft relative to a predetermined course, a receiver aboard each of said aircraft for receiving said first mentioned signals'modulated by said further signals, and a single indicator aboard each of said craft responsive to each of said receivers for translating said first mentioned signals and said further signals into unitary indications of altitude and lateral position of each of said aircraft.

21. In combination, means for establishing a similar periodically recurrent time base at each of a plurality of stations, means at each of said plurality of stations for generating a signal timed with respect to said time base in accordance with a value of measurable quantity, an indicator at each" of said stations for indicating timing of signals with respect to said time base, means for transmitting said signals from each of said stations to the remainder of said stations, and means at each station for receiving signals from the remainder of said stations and for applying said signals to the indicator at said each station, and further means at each of said stations for measuring a further measurable quantity, and for modulating said signal timed with respect to said time base in accordance with said measurement of said further quantity, said indicator at each of said stations comprising means for indicating said value of said further measurable quantity.

22. In combination, a first cathode ray tube indicator having means for generating a cathode ray beam and an indicating surface visually responsive to impact by said beam, means for recurrently and periodically causing said cathode ray beam to scan said indicating surface, said last means comprising a source of saw-tooth voltage, means for measuring the magnitude of a first physical quantity, means responsive to said last means comprising a source of saw-tooth voltage proportional to said magnitude, means resonsive Jointly to said saw-tooth voltage and to said direct current voltage for generating a first pulse timed in accordance with said magnitude, firstmeans for transmitting said first pulse to a remote location, a second cathode ray tube at said remote location having means for generating a cathode ray beam and an indicating surface visually responsive to impact by said cathode ray beam, means for recurrently and periodically causing said second named cathode ray beam to scan said second named indicating surface, said last -means comprising a source of saw-tooth voltage, means for measuring the magnitude of a further physical quantity at said remote location, means responsive to said last means for establishing a direct current voltage proportional to 20 said magnitude, means responsive jointly to said last named saw-tooth voltage and to said last named direct current voltage for generating a further pulse timed in accordance with said magnitude of a"further physical 'quantity, means for transmitting said further pulse from said remote location, means at said first cathode ray tube indicator responsive to said second pulse for modulating said cathode ray beam of said first cathode ray tube, means at said second location responsive to said first mentioned pulse for modulating said second cathode ray beam, and means for synchronizing said means for recurrently and periodically causing said cathode ray beams to scan said indicating surfaces, means for modulating saidfirst pulse in accordance with the value of still a further measurable quantity, means for modulating said further pulse in accordance with still another measurable quantity, means at said first cathode ray tube indicator responsive to said modulation for still further modulating said cathode ray beam of said first cathode ray tube, and means at said second location responsive to modulation of said first mentioned pulse for still further modulating said second named cathode ray beam.

23. In combination, a cathode ray tube indicator having an indicating surface, means for establishing recurrent traces on said surface, means responsive to initiation of each of said traces for generating a saw-tooth voltage, means for measuring the magnitude of a physical quantity and for establishing a voltage proportional to said magnitude,-means responsive to said last mentioned-voltage and to said saw-tooth voltage for generating a pulse at a time during said recurrent trace which is representative of said magnitude, means for transmitting said pulse to a remote point, and means at said remote point {or indicating said magnitude, means for measur ng the magnitude of a further physical quantity and for establishing a modulation signal representative of said-further physical quantity, and means for modulating said pulse in accordance with said further physical quantity, said means at said remote point for indicating said magnitude comprising means for simultaneously indicating said further magnitude.

24. In combination, means for establishing corresponding mutually synchronized periodically recurrent time bases at each of a plurality of aircraft, means aboard each of said aircraft for generating pulses timed with respect to said time bases in accordance with the altitude of said aircraft, means for modulating said pulses in accordance with deviations of said aircraft from a predetermined course, an indicator means on each of said aircraft for indicating timing of pulses with respect to said time base, and deviations from said course. as a unitary indication, means for transmitting said pulses from each of said aircraft to the remainder of said aircraft. and means at each of said aircraft for receiving said pulses from the remainder of said aircraft and for applying said signals to said indicator at each of said aircraft, visually to indicate the relative altitudes of said plurality of aircraft, and the deviations of said aircraft from said predetermined course.

25. In combination, means for establishing a similar periodically recurrent time base at each of a plurality of stations, means at each of said stations for generating signals timed with respect to said time base in accordance with the value of a first measurable quantity, means at indicator at each station.

21 each of said stations for generating modulating signals representative of the value of a second measurable quantity, means for modulating said first mentioned signals with said further signals, an indicator at each of said stations for indicating as a unitary indication the timing of signals applied thereto with respect to said time base and the value of said further measurable quantity as determined by said modulating signal, means for transmitting said :ignals modulated by said means for modulating from each of said stations to the remainder of said stations, means at each of said stations for receiving said transmitted signals, and means for applying signals received at each station to said 26. A method of telemetric communication from a plurality of stations to a central station, comprising the steps of: establishing a common time base at said plurality of stations and at said central station; generating a pulse at each of said plurality of stations, each of said pulses having a time position with respect to said common time base which is indicative of the value of a measurable quantity, modulating said pulses in a manner which is indicative of the value of a further measurable quantity, establishing a correspondence between time positions along said common time base and points along a line in space at said central station, indicating the time REFERENCES CITED The following references are of record in the file of this patent:

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